P311 is an 8 kDa intracellular protein highly conserved across species. P311 does not belong to any established protein family;neither has signature motifs that could suggest function. In mouse and human P311 is produced in the brain, in vascular smooth muscle [11, 24], in wound myofibroblasts [11] and their precursors, the pre-myofibroblasts [11];and in blood monocytes (research plan, figures 5 and 7). By performing telemetry studies we recently found that p311-deficient mice (P311 KOs) have pronounced systemic systolic and diastolic hypotension, without overt gross or microscopic vascular abnormalities. Echocardiographic, morphometric and myosin light chain 20 (MLC20) phosphorylation studies indicated that the hypotension is due to a decrease in vascular tone rather than the result of a vascular structural abnormality. Hypotension is accompanied by a significant downregulation in vascular TGF-[unreadable]1 level and activity, which occurs at the translation and/or degradation stage. More importantly, P311 KOs were significantly protected against the development of uninephrectomy-DOCA-induced hypertension. Pertinent to the Challenge Topic selected, additional studies showed a stable and tight correlation between vascular and monocyte P311 expression but a significant difference in P311 expression was observed between mice with different genetic background, such that CD-1 mice express over 2-fold less P311 than the BL/6 strain. Significant differences in monocyte P311 expression were also observed between human healthy volunteers. Since lack of P311 ameliorated experimentally-induced hypertension, we compared the hypertensive response in mice with low (CD-1) and high (BL/6) monocytic P311 level. This preliminary study showed that while both groups were normotensive under baseline conditions, the mice with low P311 developed significantly less severe hypertension than the mice with high P311 level (p<0.0001). Based on these preliminary observations we hypothesize that P311 plays an important role in the modulation of systemic blood pressure and that the level of P311 in peripheral blood monocytes is a useful biomarker to predict susceptibility for the development and/or severity of future hypertension. To test these hypotheses, the specific aims of this proposal are: 1. To determine whether P311 expression level and its vascular-monocyte correlation, observed in preliminary studies, change according to age and sex. 2. To determine whether the baseline level of monocyte/vascular P311 expression correlates with the severity of experimentally-induced hypertension, as suggested by preliminary studies. 3. To determine whether vascular P311 overexpression causes hypertension and/or increases the severity of experimentally-induced hypertension. The experiments proposed in aim #1 will demonstrate whether P311 level of expression in blood vessels and monocytes depends on the mice genetic background, whether it changes over time in male and female mice of same genetic background and whether its vascular level can be accurately assessed by determining P311 mRNA level in peripheral blood monocytes. The full scale experiments proposed in aim #2 and part of aim #3 will hopefully validate and expand our preliminary studies by unequivocally demonstrating that the basal P311 expression level in mice directly correlates with the hypertensive response in an experimental model of induced hypertension. If the studies proposed in aim #1 and #2 yield the expected outcomes, we could conclude that P311 expression level in monocytes can be accurately determined and represents a reliable predictor of hypertension susceptibility in mice. In such a case, the clinical usefulness of P311 as a biomarker for human susceptibility to hypertension should warrant direct exploration. Finally, the experiments proposed in aim #3 will demonstrate whether, at least in mice, high P311 levels can play a causative/contributory role in hypertension. In such a case, P311 could represent an additional target for the development of novel therapeutic approaches. PUBLIC HEALTH RELEVANCE: P311 is an 8 kDa intracellular protein of unknown function. In humans and mice P311 is produced by certain neurons, by vascular smooth muscle and by monocytes (a type of white blood cell). Based on preliminary studies, the main goal of this project is to demonstrate that baseline P311 level in blood monocytes represents a useful biomarker to predict the future development and/or severity of hypertension in mice.